A number of different motion detector systems are known. One type of motion detector utilizes ultrasonic radiation, such as described in U.S. Pat. No. 4,820,938 issued to Mix et al. In an ultrasonic motion detector, a detection field of ultrasonic radiation is generated and is monitored for Doppler shifts, which are indicative of motion. Such motion sensors are integrated with a light management system, wherein lights are turned off, turned on and/or are dimmed according to the detection of motion or a lack of detected motion.
One of the shortcomings of current motion detector systems and devices is that they typically are only effective for detecting motion in a small area and are ineffective at monitoring motion at or near walls. Accordingly, these motion detector systems and devices typically require that detector units are strategically positioned in corners of a room or in a narrow corridor, such that the detector units broadcast through the room or corridor into an area where motion is most likely to occur. Despite the strategic positioning of the detector units, such devices and systems are ineffective at monitoring motion at or near walls or through an entire room. Such systems or devices can be protrusive and unattractive.
Further, it is generally preferably to have a ultrasound motion detectors that operate at a sufficiently high frequency (about 40 KHz) such that interference with hearing aides, and the like, are minimized. Unfortunately, the energy of ultrasound waves at these higher frequencies are attenuated by air to a greater degree than lower frequencies. Accordingly, motion defectors which operate at these high frequencies can require several transducers to effectively detect motion in a room.
In view of the aforementioned shortcomings, what is need is a motion detector system and device with the flexibility to change the size and shape of the detection area and thereby giving the system the flexibility to be mounted in more places and provide better coverage with fewer sensors. Further, what is needed is a motion detector that does not interfere with hearing aids.